This invention is concerned with marine antifouling and, more particularly, with a composite material useful for cladding marine structures to provide resistance against marine fouling.
It has been known for many years that metallic copper and copper-nickel alloys have antifouling properties. However, it has often proved difficult in practice to provide copper or copper-alloy surfaces on marine structures in a manner and form such as to obtain the benefit of the antifouling properties. One problem is that, on steel marine structures, the copper must be kept out of direct electrical contact with the steel since otherwise the antifouling effect is lost. This has not always been easy to achieve reliably.
Very often, it is desired not only to confer antifouling properties on a marine structure, but also to physically protect it against corrosion. It has been found that synthetic materials such as polychloroprenes (e.g.), neoprene) and the like provide very effective protective coatings on structural members in a marine environment. Conventionally, neoprene coatings are applied to offshore structures at a factory or similar facility prior to immersion. The structural elements (e.g. tubular members); to be coated are shot blasted to a high standard of surface finish and coated with a bonding agent to assist adhesion of the neoprene to the steel substrate. They are then deployed onto a horizontal lathe which rotates the tubular member. A dispensing station moves axially along the tubular member such that the (uncured) neoprene is helically wrapped around the pipe to form a total surface coating. When only an anti-corrosion coat is required, this neoprene layer is further wrapped in a nylon or similar outer taped layer and the composite placed inside a pressure vessel and vulcanised using pressure and steam heat. The vulcanisation process cures the neoprene, which forms a very strong bond with the steel substrate and is very durable in seawater. A similar result can be achieved by using a hand lay-up technique with calendared sheets of uncured neoprene and localised heating and curing techniques.
An extension of this method has been developed to provide an antifouling coating by placing a sheet of copper or copper-nickel alloy around the uncured neoprene after suitable surface preparation and use of bonding agents. The nylon tape wrap is applied over the outer side of the sheet, and the assembly is vulcanised in the normal manner. The sheet of copper or copper-nickel is generally preformed by rolling to conform to the curvature of the tubular member prior to installation and has to be cut precisely to size: both of these preparatory processes are time consuming and labour-intensive.
Attempts to simplify this process by using a continuous length of copper or copper-nickel alloy which is wound on to the tubular member as a continuous helix are described in European specification no. 0188357A. However, in practice a number of problems arise which make this process unsatisfactory. In particular, there are varying thermal expansion and contraction rates for the copper and steel components, and the neoprene itself contracts upon cure, so that intermittent buckling of the helically wound copper surface tends to occur, with local loss of fouling protection and a puckered finish.